The invention relates to a process and apparatus for measuring the degree of pollution of aqueous liquids, for example effluents, through biodegradable components. In the process and apparatus of the invention, a partial stream is withdrawn from the liquid undergoing examination. The partial stream is oxygenated and continuously flows through a biological bath in a reaction vessel, after which its residual oxygen content is measured. In the technique of the present invention, the living mass of the bath is held at an essentially constant level.
The determination of the biological oxygen demand has heretofore generally been carried out with a standardized random sample process, in which the result is ascertained after five days (so-called BOD.sub.5). The requirements therefor are established in the "German Standard Process H 4". Continuously working apparatuses are not heretofore known.
For the determination of the toxic effects in aqueous liquids, tests with fish or bacteria cultures are usually carried out. The results of the tests provide a positive or negative indication. From DE-OS No. 2,514,609, a process and device for the measurement of the acute toxicity of aqueous liquids is known. With this process and device, it is not possible to differentiate between degradable contamination decline and low toxicity levels in, for example, effluents as only a positive or negative indication is given.